This invention relates to data entry keyboard apparatus of a type comprising an array of key switches and associated electronic logic circuits for detecting the actuation of a key switch and providing an output signal condition corresponding to an actuated key switch, in which the logic circuits have a plurality of connection leads for their interconnection with the key-switch array and include pulse sequencing means for producing in a recurrent cycle a plurality of pulse signals of different phases which are applied to successive ones of said connection leads to produce periodic active signal levels thereon, and the key switches of the array are so interconnected with each other and with said connection leads that any one of these leads can be interconnected with any other one by the actuation of an appropriate key switch, the output signal condition being determined by the active signal level of a particular pulse signal which is fed from one connection to another via an actuated key switch.
Data entry keyboard apparatus of the above type, examples of which are described in United Kingdom Patent Specification Nos. 1,415,469; 1,478,633; and 1,569,604, has use in, for example, electronic apparatus such as electronic desk and pocket calculators, and remote control modules for television receivers.
In a data entry keyboard apparatus of known type as set forth above, n/2.times.(n-1) key switches can be contained in the key-switch array, where n is the number of connection leads. Thus, for example, the total number of key switches which the array can contain when the logic circuits have six (n=6) connection leads is fifteen. In order to increase the number of key switches which the array can contain, it has hitherto been necessary to increase the number of connections that the logic circuits have for their interconnection with the array, and the increase in the number of key switches for each additional connection is very advantageous compared with conventional matrix arrays. However, this requirement of additional connections exacerbates the well-known problem that exists in the design of integrated circuits of using as few external connections as possible for interconnection between the internal circuitry of the integrated circuit and external circuitry. The fewer the number of external connections that are required, the more cost effective an integrated circuit package becomes, possibly even where additional circuitry is included in the integrated circuit in order to save an external connection.